Chemically Synthesized Lactose Operators, 21 to 40 base-pairs in length will be ligased into the Co1 E1 PMB9 plasmid and used to transform strains of E. coli. Cloned operators will be characterized as to repressor binding in vitro and in vivo. A variety of sequence alterations in the operator will be prepared by chemical means and characterized as to repressor binding. Plasmids carrying up to 10 copies of interesting operator sequences will be constructed and used to prepare large amounts of purified operator segments for physico-chemical studies.